Sorry, forgot to replace one variable (Date >> Today()):
Case(
Mod(Floor(DateDiff(Today(), Date(1901, 1, 1), "d")), 7),
4, "Sat",
5, "Sun",
6, "Mon",
0, "Tue",
1, "Wed",
2, "Thu",
3, "Fri",
"Function failed!"
)
Please let me know if this is helpful.